Terrestrial communications systems continue to provide higher and higher speed multimedia (e.g., voice, data, video, images, etc.) services to end-users. Such services (e.g., Third Generation (3G) and Fourth Generation (4G) services) can also accommodate differentiated quality of service (QoS) across various applications. To facilitate this, terrestrial architectures are moving towards an end-to-end all-Internet Protocol (IP) architecture that unifies all services, including voice, over the IP bearer. In parallel, mobile satellite systems (MSS) are being designed to complement and/or coexist with terrestrial coverage depending on spectrum sharing rules and operator choice. With the advances in processing power of desktop computers, the average user has grown accustomed to sophisticated applications (e.g., streaming video, radio broadcasts, video games, etc.), which place tremendous strain on network resources. Internet services, as well as other IP services, rely on protocols and networking architectures that offer great flexibility and robustness; however, such infrastructure may be inefficient in transporting IP traffic, which can result in large user response time, particularly if the traffic has to traverse an intermediary network with a relatively large latency (e.g., a satellite network). To promote greater adoption of data communications services, the telecommunications industry, from manufacturers to service providers, has agreed at great expense and effort to develop standards for communications protocols that underlie the various services and features.
Satellite systems, however, pose unique design challenges over terrestrial systems. That is, mobile satellite systems have different attributes that make terrestrial designs either not applicable or inefficient for satellite systems. For example, satellite systems are characterized by long delays (as long as 260 ms one-way) between a user terminal device and a base station compared to the relatively shorter delays (e.g., millisecond or less) in terrestrial cellular systems—which implies that protocols on the satellite links have to be enhanced to minimize impact of long propagation delays. Additionally, satellite links typically have smaller link margins than terrestrial links for a given user-terminal power amplifier and antenna characteristics; this implies that higher spectral efficiency and power efficiency are needed in satellite links. Moreover, the satellite transmission or channel resources represent limited resources, where the deployment of additional transmission resources is significantly more expensive, difficult and time consuming as compared with terrestrial radio resources. Accordingly, the transmission resources of a satellite system must be used efficiently to maximize the available bandwidth, in order to provide the required quality of service for the extensive and diverse assortment of service applications available to the mobile user, and to maximize the number of potential users in a system without adversely affecting the quality of service.
An IP Multicast service is a point to multipoint service, where hosts or users join an IP multicast session by using host-router protocols, such as Internet Group Management Protocol (IGMP). Traditional wireless IP networks are typically deployed based on unicast architectures and protocols. Accordingly, under a unicast framework or infrastructure, for a multicast session, each IP packet of the multicast session must be transmitted individually to each participating host via a wireless link (e.g., in a unicast or point to point manner). Such a multicast session, therefore, would utilize as many radio resources as there are hosts participating in the multicast session, which inefficiently consumes extensive radio resources for a multicast session.
Push-to-talk (PTT) services provide a method of conversing on half-duplex communication lines (including two-way radio), using a momentary button to switch from reception mode (listen mode) to transmit mode (talk mode). PTT over Cellular (PoC) provides PTT services over cellular phone networks, enabling use of a mobile phone as a two-way PTT radio (e.g., a walkie-talkie) over unlimited range (only limited by the mobile network coverage). One significant advantage of PoC/PTT services is that a single person is able to an active talk group with a single button press, without having to make several calls to coordinate with a group. The Open Mobile Alliance (OMA) PoC specifications define standardized architectures and protocols to implement a half-duplex push-to-talk service over an IP based infrastructure using voice over IP (VoIP) and using Session Initiation Protocol (SIP) for call signaling. A 3GPP packet-switched wireless network can provide the IP infrastructure over which the PoC service can be implemented.
A key feature of the 3GPP network is its ability to provide differentiated QoS for the different simultaneous packet flows using the network, which are carried on different Packet Data Protocol (PDP) bearers. In the context of a PoC service, this means that the SIP-based call signaling flow, the PoC floor control flow and the VoIP media flow each can receive the QoS best suited to it. 3GPP specifications recommend that SIP-based call signaling and PoC floor control flows should receive interactive class QoS, whereas the voice media flow should receive streaming class QoS.
Being a half-duplex service, PoC has the potential to be operated resource-efficiently because the floor control protocol guarantees that no more than one participant is allowed to speak at a time, and therefore that only one participant need be given uplink resources at any time. Similarly, all the participants receive the talker's media stream and therefore there is the potential (assuming that a common voice codec is used by all participants) to transmit this media once and have many or all participants in the same cell receive the same transmission, conserving downlink resources. Realizing these resource efficiencies for PoC in a practical 3GPP packet switched network is challenging for a number of reasons. First, QoS is decided when a PDP bearer is set up, and modifying the QoS or releasing the bearer and establishing another one requires PDP context signaling that utilizes significant radio and spectral resources. Further, when the wireless links are slow and have long propagation delays, this signaling can introduce latencies of several seconds, which would be unacceptably large if incurred each time the floor was handed over in a PoC session. Second, each PDP bearer has an associated radio bearer, which in turn is allocated its own radio resources. Accordingly, with standard 3GPP radio bearers, the PDP bearers of multiple PoC session participants cannot use the same downlink radio resource to receive a common media stream, and thus efficiencies cannot be achieved by delivering such common media streams over a single radio resource.
Currently, some mobile satellite systems (MSS) support PoC services, however, they do so using proprietary architectures and methods, and thus are not based on the OMA PoC specifications.
Example embodiments of the present invention provide system architectures and methods to solve these problems and realize resource efficiencies in PoC services over mobile wireless terrestrial and satellite communications systems as described below.